Traditional semiconductor fabrication techniques construct structures that are generally comprised of orthogonal elements. Transistors, conductors, isolators, or other structures may be visualized as a child's set of wooden building blocks. They may be placed one atop another and in appropriate cases may overlap, but when viewed from above, traditionally the top surfaces are visible while the perpendicular side surfaces are not.
While the widespread application of semiconductors exemplifies the functionality of perpendicular structures, there are known situations where the perpendicular structure is not ideal. At least two examples can be readily found with respect to liquid crystal displays and the mass production of precise nanometer scaled components.
Liquid crystal displays are growing in application as the costs of manufacturing decrease. Inherent in their growing popularity of application is also the improved ability to control polarization of the crystals comprising the display. Stated very simply, if a given crystal is polarized in one orientation it will reflect light differently then when it is polarized in a second orientation. Variations in the degree of polarization will result in variations of reflection as well.
In a typical liquid crystal display, the liquid crystal is disposed about a series of tiny pillars, the base of each being connected to a substrate that provides some form of selective electrical connectivity. When a given pillar is charged, it changes the local polarization of the liquid crystal about that pillar, The affect of the charge is most dramatic about the edges of the pillar. Much as with the example of viewing wooden blocks from above, the edges affecting the polarization of the crystal as it is viewed are the edges of the top surface of the pillar. The effect of the side surfaces is minimal as they are perpendicular and not exposed to top down viewing. While it has been understood that tilting the pillars would expose at least one side, and thereby increase the apparent polarization effect upon the crystal, difficulties in reducing pillar size and in achieving consistent precise angles have frustrated their production to date.
Throughout the history of manufacturing components in almost all cases the quality of production may be increased while costs are decreased when methods are found to simplify repetitive processes. With respect to semiconductors and nano-scaled components, the use of photolithography is well known. Generally speaking, a layer of material is set down on a substrate. A photo-resist layer, also commonly know simply as a photoresist, or even resist, is then applied typically with a spin coating machine. A mask is then placed over the photoresist and light, typically ultra-violet (UV) light, is applied. During the process of exposure, the photoresist undergoes a chemical reaction. Generally the photoresist will react in one of two ways. With a positive photoresist UV light changes the chemical structure of the photoresist so that it is soluble in a developer. What “shows” therefore goes, and the mask provides an exact copy of the pattern which is to remain. A negative photoresist behaves in the opposite manner—UV exposure causes it to polymerize and therefore photoresist dissolving by the developer. As such the mask is a photographic negative of the pattern to be left. Following the developing process “blocks” of photoresist remain. These blocks may be used to protect portions of the initial layer during further processing, may serve as isolators or other components.
In many cases, the defined structures achieved by the masked and developed photoresist are repeated many times across a given layer. The masking process and the developing process do have inherent error margins. Further, as the creation of a mask is typically complex and cost intensive, use of a single large mask to mask an entire substrate all at once may not be desired. As a result a smaller mask may be used repeatedly to achieve the affect of a single large mask, however, misalignment of the repeated maskings may waste material and/or result in an unusable wafer. In addition, the two steps of masking and developing are distinct and each may require separate devices and setup times.
To overcome some of these drawbacks, manufacturers have considered the use of nano-imprinting templates. Simply stated, a nano-imprinting template operates as a stamp, pressing three-dimensional structures into a semi soft polymer that retains a negative impression when the template is removed. As the structures provided on the template extend perpendicularly and are of a small scale, it is often difficult to affectively apply the template. Rotation of the template during application or removal is likely to damage the template and/or improperly skew the negative impression. As a result, great care must be employed to move the template in a plain directly parallel to the receiving polymer. Such movement requires that the surface tension and any inadvertent stiction or bonding between the template and the resist over the substrate be broken across the entire contacting surface at the same time. Any particulates incorporated into the resist or left behind on the template/stamp lead to eventual wearing out of the stamp and also defects in the printed resist. Thus, attention to the wear characteristics of the stamp is especially important since it is expected to be used repeatedly. While rolling the template into and out of the soft polymer would greatly reduce the stress imposed upon the surfaces, the ability to provide sufficiently strong, small and angled features upon a template has proven unreliable.
Attempts to fabricate angled features from traditional resist materials have involved either forming a “pillar” by stacking a series of smaller blocks one atop the other, each slightly offset, or exposing the photoresist at an angle so that developing occurs at an angle. In either case, the resultant pillar structures have been large, 0.4 to 0.5 microns across, and only slightly angled.
Hence, there is a need for a process of achieving angled features in nanolithography and nanoimprinting which overcomes one or more of the drawbacks identified above. The present invention satisfies one or more of these needs.